This is an invention improving the heating system fuel economizer disclosed in the parent application, referenced above. The parent application discloses a device that implements repeated burner-on cycles within the heating cycle in order to increase heat transfer efficiency and reduce fuel consumption to deliver the same heating performance. The increase in efficiency is most effectively achieved in hot-water heating systems, testing of which had indicated a fuel or energy efficiency increase of up to 50%, that is, a reduced fuel consumption for the same heating demand of up to 50%.
As with the parent invention, an improvement in heat exchange efficiency afforded by this invention is also applicable to other types of heating systems including forced air heating. However, the improvement attributable to heat transfer efficiency also afforded by this invention cannot be applied to heating systems other than hot-water heating systems where the means of heat transfer is not by circulating hot water. Thus, the level of efficiency improvement for forced air heating will not be as high as with hot-water heating systems. This is apparent when it is understood that with hot-water systems, any heat not transferred from the water to the indoor air is returned to the boiler. With forced air systems, the air passing through the heat exchanger is delivered directly into the living space and therefore not returned via a closed system.
The discussion hereinafter is limited to hot-water heating systems with the understanding that the principles discussed may be applied to other heating systems.
The improvements of the present invention have also been tested to deliver an energy efficiency increase up to about 55% over hot water heating systems operating in the traditional fashion without the fuel economizer, as improved by the present invention. The present invention, thus, represents an improvement in energy efficiency of up to 5% above the fuel efficiency delivered by the fuel economizer of the parent invention.
The level of heating in a home is usually controlled by a room thermostat which has set upper and lower temperature limits. When the indoor temperature reaches the upper limit the room thermostat shuts the boiler burner down and when the indoor temperature falls to the lower limit it brings the burner on again. A complete heating cycle comprises a burner-on stage and a burner-off stage and the duration of one cycle is the length of time between the burner coming on at the beginning of one cycle and the burner coming on at the beginning of the next cycle.
The burner-on stage of the cycle may be divided into two phases. Phase I is the initial heat-up phase and Phase II is the constant heat phase. When the burner comes on at the start of Phase I, much of the heat supplied is absorbed by the heat exchanger and the remainder is lost via the flue. The heat exchanger then passes its heat on to the circulating water.
Initially the heat exchanger is relatively cool. The difference in temperature between the hot gases and the heat exchanger is at its highest and the rate of heat absorbed is greatest. As the heat builds up in the heat exchanger, the temperature-rise of the water between the inlet and outlet of the boiler gradually increases. Eventually the temperature of the heat exchanger and the water temperature-rise reach constant values. Phase II then commences and these levels are maintained until the end of the heating period when the burner cuts out.
Testing with the fuel economizer disclosed in the parent application has proved that in practice heat otherwise lost can be reclaimed in both Phases I. and II.
The invention of the parent application works by interrupting the electrical supply to the burner while the room thermostat is still calling for heat, the burner shuts down but the circulating water pump continues to run. This means that the water, which is still circulating, absorbs the residual heat from the heat exchanger and passes it on to the indoor air with no further heat energy being supplied from the burner. After a suitable period the electrical supply is reinstated bringing the burner on again. This on/off process is repeated until the burner is shut down by the room thermostat.
In order to enable the heating system to operate in this way, the parent application teaches that a timer is installed in the electrical supply to the burner. An override thermostat is also installed so that, in extremely cold outside conditions, if the Fuel Economizer is unable to maintain the room temperature, this override thermostat will take over and bring the room temperature up to the required level, at which point the Fuel Economizer will once again take over.